JP2813712B2 - Photoelectric conversion element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photoelectric conversion element, and more particularly, to a photoelectric conversion element having a structure in which an amorphous silicon-based thin film is stacked on a surface of a crystalline semiconductor. In the present invention, a crystalline semiconductor is a monoatomic crystal such as Si or Ge, or a group IIIV compound, IIVI
Refers to a compound semiconductor such as a group compound, and an amorphous silicon-based thin film is a-Si: H, a-Si: H: F, a-Si _X Ge _1-X :
_{H, a-Si X C 1} -X: H, a-SiN Y: H ( including microcrystalline) inclusive amorphous of Si, such as say a thin film.

<Prior Art> Conventionally, an n-type amorphous silicon-based thin film has been laminated on a p-type crystalline silicon substrate to form a photoelectric conversion element or the like.
From the viewpoint that it has a sheet resistance of 0 MΩ / □ or more and cannot be used as a layer for extracting current, a transparent conductive film is further laminated on the entire surface of amorphous silicon to constitute an element.
This method of constructing an element does not require a high-temperature process for introducing impurities into the crystal, and has no potential to generate crystal defects due to the introduction of impurities, and thus has a potential for realizing a high-performance element.

<Problems to be Solved by the Invention> However, in the above-described configuration method, since the light absorption coefficient of amorphous silicon is large, there are the following problems.

That is, in order to increase the current sensitivity of the photoelectric conversion element, it is necessary to make the film thickness as small as possible. However, when the film thickness is made small, the space charge layer expands from the interface with the transparent conductive film, and the output voltage decreases. Was gone.

<Means for Solving the Problem> In order to solve the problem of the configuration of the conventional device, the present invention examined in detail the electrical characteristics of a laminated structure of an amorphous silicon-based thin film and a crystalline semiconductor. It has been found that a carrier-inducing layer can be formed on the crystal semiconductor side at the interface of the structure.

This carrier inducing layer often becomes an accumulation layer if the crystalline semiconductor and the amorphous silicon-based thin film are of the same conductivity type, and often becomes an inversion layer if the crystal semiconductor and the amorphous silicon-based thin film are of different conductivity types. Depending on the work function difference of the amorphous silicon-based thin film, even if it is of the same conductivity type, it becomes an inversion layer, and even if it is of the opposite conductivity type, it becomes a storage layer. Based on these findings, the present invention rather actively uses a carrier-inducing layer that can be steadily formed on the crystalline semiconductor surface by laminating an amorphous silicon-based thin film on the crystalline semiconductor surface, and uses this for device operation. A semiconductor device used as a necessary and constantly existing region is proposed.

According to such a configuration, in addition to being able to solve the conventional problems described above,
The device manufacturing process can be simplified, and a semiconductor device based on a new configuration principle can be provided.

Note that a third thin film such as an oxide film and a nitride film of the crystalline semiconductor may be interposed between the crystalline semiconductor and the amorphous silicon-based thin film as long as the carrier inducing layer according to the present invention can be formed.

<Operation> In the present invention, the carrier inducing layer has a sheet resistance of 1 / 10,000 or less of that of the amorphous silicon thin film. This eliminates the need for the film to directly contact the amorphous silicon-based thin film. Therefore, it is possible to make the amorphous silicon-based thin film thin without lowering the output voltage until the current loss due to light absorption is minimized.

What is important here is that the carrier-inducing layer used as a layer for passing a current with a relatively low resistance is not a metallurgically formed tangible region having a specific occupation area in the case of the present device. Nevertheless, it is equivalent to this and is used as a “region that constantly exists”. In other words, a carrier induction layer that is constantly formed by laminating an amorphous silicon-based thin film on the surface of a crystalline semiconductor can perform this function without particularly forming a region for flowing a current as a tangible region.

As a result, in the photoelectric conversion element to which the present invention is applied,
Since it is no longer necessary to attach the current extraction electrode to the entire surface of the amorphous silicon thin film as in the conventional method, the electrode may be partially provided, and the surface of the amorphous silicon thin film is further charged with a space charge layer due to contamination or the like. It has become possible to coat a protective layer such as a silicon nitride film on the surface of the amorphous silicon-based thin film so as not to cause the occurrence of the problem.

Furthermore, the transparent conductive film is often a metal oxide, and directly attaching it to the amorphous silicon-based thin film causes oxygen to be supplied to the crystal interface, deteriorating the electronic state of the interface (interface level). ), But this problem could also be solved.

When the carrier inducing layer is a storage layer, an electric field that repels minority carriers from the lamination surface with the amorphous silicon-based thin film toward the inside of the semiconductor is constantly present on the semiconductor surface due to the storage layer that is constantly present. That is, by using this, it is possible to realize an improvement in the output voltage and an improvement in the carrier collection efficiency due to the confinement of carriers in the photoelectric conversion element and the like.

On the other hand, the amorphous silicon-based thin film has a large number of tail levels and gap levels in the band, and conducts in the gap. Therefore, carriers in the carrier inducing layer can be extracted through the amorphous silicon-based thin film.
In such a case, by attaching an electrode to the amorphous silicon-based thin film, a stable and sustained ohmic contact can be obtained when the constantly formed carrier-inducing layer is an accumulation layer.

<Embodiment> FIG. 1 shows a first embodiment in which the present invention is applied to a photoelectric conversion element. Reference numeral 10 denotes a first conductivity type crystalline semiconductor (thin film, thick film, bulk crystalline Si, InP, etc.), Reference numeral 20 denotes an amorphous silicon-based thin film of the first opposite conductivity type laminated on the first surface of the crystalline semiconductor 10, and reference numeral 12 denotes an inversion that is steadily induced on the first surface of the crystalline semiconductor 10 by the amorphous silicon-based thin film 20. A layer 21, a first conductive electrode adhered to the amorphous silicon-based thin film 20, 22 a protective layer made of a silicon nitride film or the like, 30 a second layer laminated on the second surface of the crystalline semiconductor 10.
13 is a storage layer which is constantly induced on the second surface of the crystalline semiconductor 10 by the second amorphous silicon based thin film 30, and 31 is a second layer of the crystalline semiconductor 10.
Is a conductive electrode adhered to the surface of the substrate. Even if the second amorphous silicon-based thin film 30 is of the same conductivity type as the crystal semiconductor 10 and has a work function opposite to that of the crystal semiconductor 10 and the work function is in a direction that emphasizes the first conductivity type more than the Fermi level of the crystal semiconductor 10, An accumulation layer can be induced.

Now, in the embodiment of FIG. 1, it is assumed that light is incident from the first surface, as indicated by the arrow L (of course, it also operates as a photoelectric conversion element when incident from the second surface). . Minority carriers generated by the incident light, for those generated by the second near the surface as indicated by arrows C ₁ by the electric field of the storage layer, are pushed back to the first surface side.

The minority carriers pushed back enters the inversion layer 12 with minority carriers generated in the first surface near electrically conductive inversion layer 12 in a direction parallel to the first surface, as indicated by arrow C _2, the first And collected on the first conductive electrode 21 through the amorphous silicon-based thin film 20. On the other hand, the current due to the majority carriers generated by light reaches the second near the surface as indicated by arrow C _3, a portion passes through the accumulation layer 13, parallel to and conducted to the second surface, the second Collected on the conductive electrodes. In the first embodiment of the present invention, the thickness of the first amorphous silicon-based thin film 20 can be made thinner than in the conventional example without reducing the output voltage, so that the sensitivity to short wavelength light is improved, and Since the electronic state of the surface of the first crystal semiconductor is good (the interface state density is low), the first crystal semiconductor is excellent in short-wavelength sensitivity and output voltage. Second conductive electrode 31
Is adhered to the crystalline semiconductor 10 in this embodiment. This is because the resistance in the thickness direction of the second amorphous silicon-based thin film 30 is large enough to impair device characteristics, or the crystalline semiconductor 10 and the second amorphous silicon thin film 30 are bonded to each other. Necessary when a third insulating thin film is interposed between the silicon-based thin films 30,
The second conductive electrode 31 is in ohmic contact with the crystal semiconductor 10.

When the resistance in the thickness direction of the second amorphous silicon-based thin film 30 is small, the second conductive electrode 31 can be directly bonded to the second amorphous silicon-based thin film 30.

FIG. 2 shows a second embodiment of the present invention. The difference from FIG. 1 is that when the first conductive electrode 21 is directly bonded to the first amorphous silicon thin film 20, the first amorphous silicon thin film is formed. A configuration taken when the resistance in the film thickness direction of No. 20 is large or the resistance between the inversion layer 12 and the electrode is large due to the interposition of the third insulating thin film is shown. The region 14 is a carrier collection region of the opposite conductivity type formed on the first surface of the crystalline semiconductor 10 having the first conductivity type. The carriers of the inversion layer are first collected in this region, and then the carrier collection region 14 It is taken out by the bonded first conductive electrode 21C. The minority carriers are pushed back on the second surface of the crystalline semiconductor 10,
The operation taken out through the inversion layer 12 is the same as in the embodiment of FIG. Note that the first conductive electrode 21C is a crystal semiconductor 1
In the case of forming a barrier with the first surface of 0, current can be extracted without providing the carrier collection region 14.
The storage layer 13 is provided on the second surface of the crystal semiconductor 10 of the second embodiment.
(For example, of the same conductivity type) is stacked. Further, on the surface of the second amorphous silicon-based thin film 30, a transparent conductive film 32 and a conductive electrode 31b are sequentially laminated. This structure is effective when the resistance in the thickness direction of the second amorphous silicon thin film 30 is small, the arrow L ₁ from the first surface
As shown in (2), the incident light is effectively reflected by the laminated structure on the second surface, returns to the crystalline semiconductor 10 again, and is effectively absorbed. Therefore, the long-wavelength sensitivity is improved.

<Effects of the Invention> As described above, according to the present invention, it is possible to manufacture a photoelectric conversion element having excellent short-wavelength and long-wavelength sensitivity. Since some can be constituted by a carrier induction layer which is constantly formed according to the present invention, steps and devices for the steps which were necessary in order to actually have to actually make a region to be replaced by the carrier induction layer, There is a special effect that materials and the like can be omitted.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are block diagrams of the first and second embodiments of the present invention, respectively.

Claims (2)

(57) [Claims] 1. A photoelectric conversion element having a structure in which an amorphous silicon-based thin film is laminated on opposing first and second surfaces of a crystalline semiconductor, wherein the amorphous silicon-based thin film laminated on the first surface serves as a first element. Electrically inducing a carrier-inducing layer on the crystal surface of the amorphous silicon-based thin film, partially providing an electrode on the amorphous silicon-based thin film, Flowing out in the direction, and electrically inducing a carrier accumulation layer on the second crystal surface by the amorphous silicon-based thin film laminated on the second surface, and forming a conductive electrode on the amorphous silicon-based thin film. Repelling minority carriers on the second crystal surface toward the inside of the crystal semiconductor by an electric field existing in the carrier accumulation layer. The photoelectric conversion element characterized. 2. An insulating thin film such as an oxide film or a nitride film of a crystalline semiconductor is provided between the crystalline semiconductor and the amorphous silicon-based thin film laminated on the first surface or the second surface. The photoelectric conversion element according to claim 1, wherein